1. Field of the Invention
The present invention relates to a method of manufacturing a liquid ejection head including a nozzle plate for liquid ejection.
2. Description of the Related Art
Liquid ejection heads are widely used for a variety of purposes ranging from image recording to industrial purposes, such as drawing a wiring pattern with liquid containing a conductive material. Particularly, liquid ejection heads from which liquid is ejected by driving a piezoelectric member are widely used because these heads are capable of ejecting various kinds of liquid. There is a growing need for liquid ejection heads to achieve higher-density and higher-accuracy ejection. A typical liquid ejection head includes a nozzle plate having a plurality of ejection ports for liquid ejection and a cavity substrate joined to the nozzle plate. The cavity substrate has pressure chambers communicating with the ejection ports and passages. In this liquid ejection head, applying pressure to the pressure chamber ejects liquid from the ejection port. Many of nozzle plates include a silicon substrate having ejection ports processed by dry etching or the like based on requests to define an ejection port diameter with high accuracy. A variation in thickness of the nozzle plate causes a variation in flow resistance of liquid to be ejected from the ejection ports. The nozzle plate accordingly should have little variation in thickness. If liquid to be ejected is alkaline ink, the ink may corrode silicon. Accordingly, part, including an inner wall of each ejection port, exposed to the ink is typically coated with an ink-resistant protective film.
Japanese Patent Laid-Open No. 2012-96499 discloses a method of manufacturing a nozzle plate including a silicon-on-insulator (SOI) substrate having a structure in which silicon films sandwich a silicon oxide film functioning as an ink-resistant protective film. The nozzle plate disclosed in Japanese Patent Laid-Open No. 2012-96499 includes a water-repellent film disposed on an ejection surface having openings of ejection ports. This water-repellent film prevents adhesion of ink to the ejection surface, thus increasing liquid ejection stability.
According to the method disclosed in Japanese Patent Laid-Open No. 2012-96499, the water-repellent film is formed on the nozzle plate by dip coating or evaporation as a final step of the method. Disadvantageously, the water-repellent film may be disposed on an inner wall of each ejection port as well as the ejection surface at completion of the nozzle plate. The water-repellent film on the inner wall of the ejection port may interfere with straight flow of liquid through the ejection port, causing a variation in flying direction of the liquid.